A common method for the manufacture of asphalt shingles is the production of a continuous strip of asphaltic shingle material followed by a shingle cutting operation which cuts the material into individual shingles. In the production of asphaltic strip material, either an organic felt or a glass fiber mat is passed through a coater containing liquid asphaltic material containing filler at a very hot temperature to form a tacky coated asphaltic strip. Subsequently, the hot asphaltic strip is passed beneath one or more granule applicators which apply the protective surface granules to the asphaltic strip material. Typically, the granules are dispensed from a hopper at a rate which can be controlled by making manual adjustments on the hopper. A typical shingle manufacturing process continuously manufactures the shingle material in a width sufficient for cutting the material into three, four or six shingles.
Prior to the shingle cutting stage, the granules are pressed into the still warm asphalt through a granule pressing means, such as a wringer-type granule press. Subsequently, the granule-covered roofing material is cooled so that the shingle cutting operation can operate on relatively cool shingle material.
One of the problems with granule-covered asphalt shingles is the problem known as "shading". Shading is defined as the tendency of a shingled roof to have certain areas which sometimes appear darker or lighter than the surrounding areas when the roof is viewed from different angles or under different light conditions. Shading is believed to result from slight variations in texture which occur during normal shingle production. The variation in texture necessary to cause shading with black or other dark colors is so slight that it cannot normally be detected during the manufacturing process. When light is reflected from certain roofs, the appearance varies as the viewer walks past the building. The impact will depend on the position of the sun and the overall light intensity. When the sun is directly overhead the shading may disappear.
It is believed that shading is caused by variation in the surface texture, and the angle, amount and direction of light reaching the roof - and the position from which the roof is viewed. A shaded appearance can also result from over or under embedment of the granules, or from mixing products from two manufacturing plants on the same roof. In summary, shading occurs when the roof appears to have color variation when viewed from a certain angle or at a particular time of day.
Previous attempts to eliminate shading problems have not been successful. Each year, replacement of numerous roofing applications is required because of shading complaints. Although shading does not affect the durability or performance of granule-covered asphalt shingles, the optical effect of shading is a serious problem in the residential roofing market.